The present invention relates to a video camera system whose lens assemblies are interchangeable.
Conventionally, a so-called hill-climbing method is known as the method of an automatic focusing (AF) device used in video apparatuses such as video cameras. The method performs focusing by extracting a high-frequency component from a video signal obtained by an image sensing device such as a CCD and driving a taking lens such that the mountain-like characteristic curve of this high-frequency component is a maximum.
This automatic focusing method requires no special focusing optical members and has an advantage in that an object can be accurately focused regardless of whether the distance to the object is long or short. An example in which an automatic focusing method of the above sort is applied to an interchangeable lens video camera will be described below with reference to FIG. 24.
Referring to FIG. 24, in a lens assembly 816, a variable power lens 802 and a compensating lens 803 are connected by a mechanical cam (not shown). When a zooming operation is manually or electrically performed, the variable power lens 802 and the compensating lens 803 integrally move.
These variable power lens 802 and compensating lens 803 are called zoom lenses.
In this lens system, a front lens 801 which is closest to an object when the image is taken is a focus lens. The focus lens 801 moves in the direction of an optical axis to perform focusing.
An image of light transmitting through these lenses is formed on the image sensing surface of an image sensing device 804 of a camera 817, photoelectrically converted into an electrical signal, and output as a video signal.
This video signal is sampled-and-held by a CDS/AGC circuit 805 constituted by a correlated double sampling circuit and an auto gain control circuit, amplified to a predetermined level, and converted into digital video data by an analog/digital (A/D) converter 806. The digital video data is input to the process circuit (not shown) of the camera 817 and converted into a standard TV signal. The data is also input to a bandpass filter (to be referred to as a BPF hereinafter) 807.
The BPF 807 extracts a high-frequency component which changes in accordance with the focus state from the video signal. A gate circuit 808 extracts only a video signal corresponding to a portion which is set as a focus detection area in a picture frame. A peak hold circuit 809 holds a peak of the video signal at an interval synchronizing with an integral multiple of a vertical sync signal, thereby generating a focus state evaluation value (to be referred to as an AF evaluation value hereinafter) representing the in-focus degree in the automatic focusing operation.
The AF evaluation value is fetched by an AF control microcomputer (to be referred to as a main body AF microcomputer hereinafter) 810 on the camera main body 817 side. The main body AF microcomputer 810 determines the focusing speed, i.e., a focus motor speed in accordance with the in-focus degree and the driving direction of the focus motor along which the AF evaluation value increases. The main body AF microcomputer 810 sends the speed and direction of the focus motor to a lens control microcomputer of the lens assembly 816.
A lens microcomputer 811 controls a focus motor 813 through a motor driver 812 in accordance with an instruction from the main body AF microcomputer 810 to drive the focus lens 801 along the optical axis, thereby performing the focusing operation.
The main body AF microcomputer 810 also determines the driving directions and the driving speeds of the variable power lens 802 and the compensating lens 803, which constitute zoom lenses, in accordance with the operation state of a zoom switch 818. The main body AF microcomputer 810 transmits these driving directions and driving speeds to a zoom motor driver 814 of the lens assembly 816. The lens assembly side calculates the driving information of a zoom motor 815 in accordance with the zoom speed and direction information sent from the camera main body side and drives the zoom motor 815 through the motor driver 814, thereby driving the variable power lens 802 and the compensating lens 803.
The camera main body 817 can be detached from the lens assembly 816 and connected to another lens assembly. This widens the sensing range.
In recent popular cameras integrated with video recorders for consumers having the above structure, the front lens is fixed while the focus lens is arranged behind the variable power lens, and the cam for mechanically connecting the compensating lens to the variable power lens is no longer used in order to miniaturize a camera and enable sensing at a close distance such as when an object is just in front of the lens. In these cameras, the locus of movement of the compensating lens is previously stored as lens cam data in a microcomputer, and the compensating lens is driven in accordance with this lens cam data. Also, a focusing operation is performed by using this compensating lens. Lenses of this type, i.e., so-called inner focus type (rear focus type) lenses have become most popular.
A zooming operation by such an inner focus type lens will be described below.
FIG. 25 is a view schematically showing the arrangement of a general inner focus type lens system.
Referring to FIG. 25, reference numeral 901 denotes a fixed first lens group; 902, a second lens group for performing a zooming operation; 903, an iris stop; 904, a fixed third lens group; 905, a fourth lens group (to be referred to as a focus lens hereinafter) having both a focusing function and a so-called compensator function of compensating for the movement of a focal plane caused by zooming; and 906, an image sensing device.
As is well known, in the lens system as illustrated in FIG. 25, the focus lens 905 has both the compensating function and the focusing function. Accordingly, the position of the focus lens 905 for focusing an image on the image sensing surface of the image sensing device 906 changes in accordance with the object distance even at the same focal length.
FIG. 26 shows the result of continuous plotting of the position of the focus lens 905 for focusing an image on the image sensing surface while the distance between the focus lens 905 and the object is changed at different focal lengths.
During the zooming operation, one of the loci shown in FIG. 26 is selected in accordance with the object distance, and the focus lens 905 is moved to trace that focus. This allows a zooming operation free from a blur.
In a conventional front lens focus type lens system, compensating lens is provided independently of a variable power lens, and the variable power lens and the compensating lens are coupled by a mechanical cam ring. A manual zoom knob, for example, is formed on this cam, and the focal length is manually changed. Even if the knob is moved as fast as possible, the cam rotates to trace the movement of the knob, and the variable power lens and the compensating lens move along a cam groove for holding the cam. Therefore, no blur is caused by the above operation as long as the focus lens is focused on an object.
In controlling the inner focus type lens system, however, a plurality of pieces of locus information shown in FIG. 26 are stored in some format (the locus itself or a function of a lens position as a variable). In general, one of the loci is selected in accordance with the positions of the focus lens and the variable power lens, and a zooming operation is performed while tracing the selected locus.
FIG. 28 is a graph for explaining one invented locus tracing method. In FIG. 28, reference symbols Z0, Z1, Z2, . . . , Z6 denote the positions of the variable power lens; and a0, a1, a2, . . . , a6 and b0, b1, b2, . . . , b6, representative loci stored in the microcomputer.
Also, p0, p1, p2, . . . , p6 denote loci calculated on the basis of the above two loci. This locus calculation is done by the following equation:
p(n+1)=|p(n)xe2x88x92a(n)|/|b(n)xe2x88x92a(n) |*|b(n+1)xe2x88x92a(n+1)|+a(n+1) xe2x80x83xe2x80x83(1)
In equation (1), if, for example, the focus lens is at p0 in FIG. 28, the ratio at which p0 internally divides a line segment b0-a0 is calculated, and the point at which a line segment b1-a1 is internally divided by this ratio is given as p1. The focus lens moving speed for holding the in-focus state can be known from this positional difference (p1xe2x88x92p0) and the time required for the variable power lens to move from Z0 to Z1.
An operation when there is no such limitation that the stop position of the variable power lens must be on a boundary having the previously stored representative locus data will be described below.
FIG. 29 is a graph for explaining an interpolation method along the direction of the variable power lens position. FIG. 29 extracts a part of FIG. 28, and the position of the variable power lens is not limited to the previously stored positions, so that the variable power lens can take any arbitrary position.
In FIG. 29, the ordinate indicates the focus lens position, and the abscissa indicates the variable power lens position. The representative locus positions (the focus lens positions with respect to the variable power lens positions) stored in the microcomputer are represented as follows for various object distances with respect to variable power lens positions Z0, Z1, . . . , Zkxe2x88x921, Zk, . . . , Zn:
a0, a1, . . . , akxe2x88x921, ak, . . . , an
b0, b1, . . . , bkxe2x88x921, bk, . . . , bn
If the variable power lens position is Zx not on a zoom boundary and the focus lens position is Px, ax and bx are calculated as follows:
ax=akxe2x88x92(Zkxe2x88x92Zx)*(akxe2x88x92akxe2x88x921)/(Zkxe2x88x92Zkxe2x88x921)xe2x80x83xe2x80x83(2)
bx=bkxe2x88x92(Zkxe2x88x92Zx)*(bkxe2x88x92bkxe2x88x921)/(Zkxe2x88x92Zkxe2x88x921)xe2x80x83xe2x80x83(3)
That is, ax and bx can be calculated by internally dividing data having the same object distance of the four stored representative locus data (ak, akxe2x88x921, bk, and bkxe2x88x921 in FIG. 29) by the internal ratio obtained from the current variable power lens position and the two zoom boundary positions (e.g., Zk and Zkxe2x88x921 in FIG. 29) on the two sides of the current variable power lens position.
In this case, pk and pkxe2x88x921 can be calculated, as shown in equation (1), by internally dividing data having the same focal length of the four stored representative data (ak, akxe2x88x921, bk, and bkxe2x88x921 in FIG. 29) by the internal ratio obtained from ax, px, and bx.
When zooming is performed from wide to telephoto, the focus lens moving speed for holding the in-focus state can be known from the positional difference between the focus position pk to be traced and the current focus position px and the time required for the variable power lens to move from Zx to Zk.
When zooming is performed from telephoto to wide, the focus lens moving speed for holding the in-focus state can be known from the positional difference between the focus position pkxe2x88x921 to be traced and the current focus position px and the time required for the variable power lens to move from Zx to Zkxe2x88x921. The locus tracing method as described above is invented.
When AF control is performed, it is necessary to trace the locus while maintaining the in-focus state. When the variable power lens moves in a direction from telephoto to wide, the diverged loci converge as can be seen from FIG. 26. Therefore, the in-focus state can be maintained by the above locus tracing method.
In a direction from wide to telephoto, however, a locus which the focus lens in the point of convergence is to trace is unknown. Consequently, the in-focus state cannot be maintained by the locus tracing method as above.
FIGS. 30A and 30B are graphs for explaining one locus tracing method invented to solve the above problem. In each of FIGS. 30A and 30B, the abscissa indicates the position of a variable power lens. In FIG. 30A, the ordinate indicates the level of a high-frequency component (sharpness signal) of a video signal as an AF evaluation signal. In FIG. 30B, the ordinate indicates the position of a focus lens.
Assume that in FIG. 30B, a focusing cam locus is a locus 604 when a zooming operation is performed for a certain object.
Assume also that a tracing speed with respect to a locus indicated by lens cam data closer to a wide side than a zoom position 606 (Z14) is positive (the focus lens is moved to the closest focusing distance), and that a tracing speed with respect to a locus indicated by lens cam data when the focus lens is moved in the direction of infinity on a telephoto side from the position 606 is negative.
When the focus lens traces the locus 604 while being kept in the in-focus state, the magnitude of the sharpness signal is as indicated by 601 in FIG. 30A. It is generally known that a zoom lens kept in the in-focus state has an almost fixed sharpness signal level.
Assume that in FIG. 30B, a focus lens moving speed for tracing the focusing locus 604 during a zooming operation is Vf0. When an actual focus lens moving speed is Vf and a zooming operation is performed by increasing or decreasing Vf with respect to Vf0 for tracing the locus 604, the resulting locus is zigzagged as indicated by reference numeral 605.
Consequently, the sharpness signal level so changes as to form peaks and valleys as indicated by reference numeral 603. The magnitude of the level 603 is a maximum at positions where the loci 604 and 605 intersect (at even-numbered points of Z0, Z1, . . . , Z16) and is a minimum at odd-numbered points where the moving direction vectors of the locus 605 are switched.
Reference numeral 602 denotes a minimum value of the level 603. When a level TH1 of the value 602 is set and the moving direction vectors of the locus 605 are switched every time the magnitude of the level 603 equals the level TH1, the focus lens moving direction after switching can be set in a direction in which the movement approaches the in-focus locus 604.
That is, each time an image is blurred by the difference between the sharpness signal levels 601 and 602 (TH1), the moving direction and speed of the focus lens are so controlled as to decrease the blur. Consequently, a zooming operation by which a degree (amount) of blur is suppressed can be performed.
The use of the above method is effective even in a zooming operation from wide to telephoto, as shown in FIG. 26, in which converged loci diverge. That is, even if the in-focus speed Vf0 is unknown, the switching operation is repeated as indicated by 605 (in accordance with a change in the sharpness signal level) while the focus lens moving speed Vf is controlled with respect to the tracing speed (calculated by using p(n+1) obtained from equation (1)) explained in FIG. 28. As a consequence, it is possible to select an in-focus cam locus by which the sharpness signal level is not decreased below the level 602 (TH1), i.e., a predetermined amount or more of blur is not produced.
Assuming a positive compensating speed is Vf+ and a negative compensating speed is Vfxe2x88x92, the focus lens moving speed Vf is determined by
Vf=Vf0+Vf+xe2x80x83xe2x80x83(4)
Vf0+vfxe2x88x92xe2x80x83xe2x80x83(5)
In order that no deviation is produced when the tracing locus is selected by the above method of zooming operation, the compensating speeds Vf+ and Vfxe2x88x92 are so determined that the internal angle of the two vectors of Vf obtained by equations (4) and (5) is divided into two equal parts by the direction vector of Vf0.
FIG. 31 is a table showing table data of locus information stored in the microcomputer. FIG. 31 shows in-focus lens position data A (n,v) which changes depending on the zoom lens position at different object distances. The object distance changes in the column direction of a variable n, and the zoom lens position (focal length) changes in the row direction of a variable v.
In this case, n=0 represents an object distance in the direction of infinity. As the variable n becomes large, the object distance changes to the closest focusing distance, and n=m represents an object distance of 1 cm.
On the other hand, v=0 represents a zoom lens position at the wide end. As the variable v becomes large, the focal length increases. Additionally, v=s represents a zoom lens position at the telephoto end.
Therefore, table data of one column corresponds to one cam locus. Locus information shown in FIG. 31 is prepared as zoom tracking data on the basis of an optical design value. With an actual lens, a locus corresponding to the design value cannot be obtained because of, e.g., an error in focal length of each lens group.
More specifically, to execute the locus tracing operation free from a blur as described above, the coordinate axes of an actual lens must match those of the table data.
An actual video camera performs an adjustment operation to determine the telephoto and wide ends of the variable power lens in data stored in advance.
A focusing adjustment method is conventionally performed, in which the operation stroke of a variable power lens from the telephoto end to the wide end is kept to be the design value. The in-focus position difference (balance) between the focus lens at the telephoto end and that at the wide end within an adjustment distance (e.g., ∞) is also set to be the design value, thereby defining the telephoto and wide ends. This adjustment method will be referred to as xe2x80x9cfixed stroke adjustmentxe2x80x9d.
Another focusing adjustment method is known, in which the difference (balance) between the in-focus position of a focus lens at the telephoto end and that at the wide end is set to be a design value. In addition, a variable power lens position is obtained, at which the uppermost position of the focus lens at the middle (intermediate focal length) on the map as shown in FIGS. 26 and 27 and the moving amount of the focus lens from the telephoto end equal the design values, and defining the telephoto and wide ends of the variable power lens. This method will be referred to as xe2x80x9ctelephoto-middle tracking adjustmentxe2x80x9d. xe2x80x9cFixed stroke adjustmentxe2x80x9d and xe2x80x9ctelephoto-middle tracking adjustmentxe2x80x9d performed using a lens group having an error in a direction of increasing the position of the focus lens when the telephoto end position and the wide end position are set at not the design values but the intermediate focal length will be described below with reference to FIG. 27.
In FIG. 27, the abscissa indicates the position of a variable power lens (i.e., a focal length), and the ordinate indicates the position of a focus lens. A locus Sb corresponds to a design locus. An actual focus lens exhibits a locus Sa. At this distance (e.g., ∞), the difference between the in-focus position of the focus lens at a telephoto end T and that at a wide end W is zero.
If the locus corresponds to the design value, and telephoto-middle tracking adjustment is to be performed, a point {circle around (1)} on the map is a start point for adjustment. The focus lens is lowered downward in FIG. 27 by a design moving amount A of the focus lens. This position is indicated by {circle around (2)}. From this state, the variable power lens is moved to obtain an in-focus position {circle around (5)} which is defined as a variable power lens position Tb at the telephoto end.
In this example, the difference between the in-focus position of the focus lens at the wide end and that at the telephoto end is zero, as described above. Therefore, the variable power lens is moved in a similar manner, and an in-focus position {circle around (6)} is defined as a variable power lens position Wb at the wide end.
When telephoto-middle tracking adjustment is to be performed for a lens having the locus Sa with an error, the focus lens is lowered from a start point {circle around (1)}xe2x80x2 for adjustment downward in FIG. 27 by the design value A, thereby obtaining a position {circle around (2)}xe2x80x2.
In a similar manner, the variable power lens is moved to an in-focus position. Consequently, a telephoto end Ta can be determined at a position {circle around (1)}, and a wide end Wa can be determined at a position {circle around (1)}. In this case, variations in focal length are generated. However, since the error of the locus Sa can be absorbed during zooming, a zooming operation free from a blur can be realized.
In fixed stroke adjustment, the stroke and the balance are adjusted to be predetermined values regardless of whether the locus Sb corresponding to the design value is exhibited or the locus Sa with an error is obtained. In both the cases, the telephoto end position is {circle around (1)}, and the wide end position is {circle around (1)}, so no variations in focal length are generated. However, the error of the locus Sa cannot be completely absorbed, and the locus Sb is traced during the zooming operation, resulting in a blur corresponding to the error.
However, the camera system as described above has a function of controlling automatic focusing in the camera main body, and its lens assemblies are interchangeable. When the response for automatic focusing or the like is determined to be optimum for a specific lens, another lens may not exhibit optimum performance. Hence, it is difficult to set optimum performance for all attachable lenses.
A technique of transmitting a focus signal necessary to execute focusing from the camera main body to the lens assembly while the function of controlling automatic focusing is assigned to the lens assembly side has been proposed.
In this case, a means for determining the size of an extraction area where a focus signal is extracted from a video signal is arranged on the lens assembly side such that the optimum response for automatic focusing for all connectable lenses can be determined. The size information is transferred to the main body side, and an appropriate size is set in correspondence with the focal length of each lens, thereby optimizing the focus signal level obtained from the camera main body.
Assume that the extraction area is fixed with respect to the frame size regardless of the types of lenses. For a wide angle lens, various objects are present in the area, so that the focus signal level tends to be high. For a high-luminance object, the signal obtained by an image sensing device is saturated, so focusing can hardly be appropriately performed. For a telephoto lens, an object image is enlarged, so that the focus signal level tends to be low. For a low-luminance object, resultant AF characteristics do not exhibit a desired result.
However, in a camera whose lenses are interchangeable and whose function of controlling automatic focusing as in the prior art is arranged in the lens assembly, the image sensing state on the main body side cannot be recognized by the automatic focusing means in the lens assembly, resulting in the following problems.
{circle around (1)} When a sensing operation is performed using an illumination equipment such as a home fluorescent lamp using discharge as a light source, discharge repeatedly occurs or stops depending on the frequency of the AC power supply of the light source, i.e., a so-called flicker is generated, so the output level of the image sensing signal sometimes periodically changes. However, the presence/absence of a flicker cannot be recognized on the lens assembly side. During focusing, it can hardly be determined whether the change in AF evaluation value is caused by the movement of the focusing lens or by a flicker, so the in-focus direction may be erroneously set.
When, to eliminate the influence of a flicker, the timing for driving the lens or fetching the AF evaluation value is always synchronized with the flicker period, the AF response becomes slow.
{circle around (2)} When a low-luminance object is to be taken, the image sensing signal is amplified by AGC. At this time, noise is also amplified, and many noise components are contained in the AF evaluation value. The amplification amount is unknown on the lens assembly side, so an erroneous operation is caused by the influence of noise in reactivation determination for a focusing operation or determination of a hill-climbing direction, often resulting in a blur.
{circle around (3)} In a sensing operation using a so-called program mode in which the iris stop, the shutter, AGC, and the like are automatically adjusted to realize effective sensing, and an optimum sensing state is realized, the exposure state changes depending on a change in mode. However, the change in mode cannot be recognized on the lens assembly side.
When the program mode changes, the AF evaluation value also changes to result in an erroneous AF operation. Particularly, when the mode changes in an in-focus state to forcibly open the iris stop for a photographic effect, the depth of field becomes small. However, when the field angle is wide, or when a high-luminance object is to be taken, an overexposure state is set, and the image sensing signal level may exceed the dynamic range of the image sensing device. At this time, the AF evaluation value does not change before and after the mode change. Therefore, an out-of-focus state is easily generated because of the decreased depth of field.
The lens assembly itself drives the iris stop in accordance with a control command from the camera main body, so that the iris stop state can be recognized. However, it cannot be determined whether the iris stop state optimizes exposure or aims a photographic effect.
If the iris stop state changes, the focusing operation may be reactivated to eliminate the above disadvantages. However, if the reactivation operation is performed every time the iris stop state changes, the AF operation is performed restlessly. {circle around (4)} In sensing using a so-called slow shutter, i.e., when the charge accumulation time in the image sensing device is prolonged to an integral multiple of the normal accumulation time, and an image sensing signal is intermittently read out, the focus signal sent from the camera main body is not updated for a time corresponding to the read period. However, the read period is unknown on the lens assembly side. Since the focus signal does not change for a predetermined time, erroneous determination of an in-focus state is made, or the hill-climbing direction is erroneously determined. {circle around (5)} In sensing using an enlargement function such as electronic zooming, the enlargement magnification and the position of enlargement in a picture frame cannot be recognized on the lens assembly side. In some cases, the focus signal extraction area becomes larger than the enlarged area. At this time, focusing is sometimes performed with respect to an object-outside-the monitor.
When the picture frame is enlarged, even a blur within the depth of field becomes visible. Therefore, a blur generated by a fine driving operation such as a wobbling operation which is performed to determine an in-focus direction becomes visible.
Additionally, the design value A necessary for the focusing operation must be set in correspondence with each interchangeable lens.
When a new lens assembly is developed, an old camera main body may not perform sufficient control.
A rear focus lens has a lot of complex cam loci, and the lens must accurately trace these loci. For this reason, the positions of the zoom lens and the focus lens must be accurately detected. For this purpose, a technique of performing feedback loop control using an encoder for position detection is available. However, a highly precise encoder is expensive and also requires a space.
A technique has been proposed instead in which the lens is driven by a stepping motor, and a moving amount of the stepping motor from a reference position is detected by counting supplied step pulses. According to this technique, the stepping motor is controlled by the microcomputer. Therefore, only by increasing/decreasing the counter value in the microcomputer, the function of an encoder can be realized, though it is open-loop control.
However, at the start time, an initialization operation must be performed to temporarily drive the lens to the reference position and reset the counter. If the power supply is turned off, and the microcomputer is reset, the contents in the counter are cleared, so that the control information including the absolute positions of the variable power lens and the compensating lens also returns to an initial value.
Therefore, even when a focusing operation is completed before the power supply is turned off, a deviation from the in-focus state is generated at the time of repowering.
In addition, when a zooming operation is performed in this state, a cam locus different from that before turning off the power supply is traced because the absolute lens position information changes. For this reason, the focusing operation must be performed again every time the power supply is turned on.
To manage the compensating lens and the variable power lens with a microcomputer, the positions of the focus lens and the variable power lens must always be recognized as absolute positions. Therefore, when the power supply is turned on, the initialization operation must be performed. When the power supply is turned off, a post-processing operation-must be-performed.
When the power supply is turned on, the focus lens or the variable power lens is moved to the infinite end or the wide end as a predetermined position (reset position), and the absolute position is recognized by the lens microcomputer such that the position matches P(0,0) in FIG. 26.
This is the initialization operation for the focus lens or the variable power lens. To perform the initialization operation at a high speed, the position of the focus lens or the variable power lens is stored in the microcomputer as post-processing at the time of turning off the power supply, and the focus lens or the variable power lens is moved close to the reset position. At the time of repowering, the initialization operation is performed, and then, the focus lens or the variable power lens is moved again to the position stored in the lens microcomputer. With this operation, sensing can be started in the same situation as before turning off the power supply.
However, when the power supply circuit of the lens is immediately turned on/off in a manner interlocked with the ON/OFF operation of the power which is supplied from the camera main body, when a video signal is output simultaneously with the ON operation of the power supply of the camera main body, or when the operating members arranged on the lens side are enabled simultaneously with the ON operation of the power supply of the camera main body, sensing is started before the lens initialization operation is completed, resulting in a blur in image or a degradation in image quality. In addition, if the power supply is turned off before lens post-processing is completed, control is confused at the time of repowering, and a long time is required to restore a normal state.
The present invention has been made to solve the above problems, and has as its object to provide an interchangeable lens video camera system which can stably focus on a main target object under any conditions of the object or the environment.
According to the present invention, there are provided a video camera system, and a camera and a lens assembly, which constitute the system, as will be described below.
That is, there is provided a camera detachably having a lens assembly including a lens for forming an image of an object and lens control means for controlling the lens, comprising:
image sensing means for converting the image of the object into an image signal and outputting the image signal; and
control means for generating information associated with an image sensing state of the object on the basis of the image signal obtained by the image sensing means and transmitting the information to a lens assembly.
There is also provided a lens assembly detachably attached to a camera having image sensing means for photoelectrically converting incident light to sense an image and outputting an image signal, comprising:
a lens for forming an image of an object;
memory means which stores locus information of the lens in advance; and
control means for receiving information associated with an image sensing state of the object from the camera and controlling the lens on the basis of the locus information and evaluation information representing a focus state of the image signal included in the information associated with the image sensing state.
Preferably, the memory means stores design position information of the variable power lens and the focus lens and the control means further comprises adjusting means for adjusting an operation of the focus lens on the basis of the position information to compensate for a movement of an in-focus point caused by the zooming operation of the variable power lens.
For example, the adjusting means-adjusts an operation stroke of the variable power lens to change a telephoto end position and a wide end position, and calculates a position of the variable power lens, at which an in-focus position of the focus lens and a moving amount of the focus lens from the telephoto end position equal those of the design position information, thereby changing the telephoto end position and the wide end position.
There is also provided a camera detachably having a lens assembly, comprising:
image sensing means for photoelectrically converting incident light to sense an image and transmitting an image signal to the lens assembly.
There is also provided a lens assembly detachably attached to a camera having image sensing means for sensing an image of an object and outputting an image signal, comprising:
a variable power lens for performing a zooming operation;
a focus lens for performing a focusing operation and compensating for a movement of an in-focus point caused by the zooming operation of the variable power lens;
memory means which stores position information of the variable power lens and the focus lens;
focus detection means for receiving the image signal and extracting, from the image signal, evaluation information which changes in accordance with a focus state; and
control means for controlling the variable power lens and the focus lens on the basis of the position information stored in the memory means and the evaluation information obtained by the focus detection means.
Preferably, the image signal is normalized in accordance with the focus state.
There is also provided a lens assembly detachably attached to a camera having image sensing means for sensing an image of an object and outputting an image signal, comprising:
a variable power lens for performing a zooming operation;
a focus lens for performing a focusing operation and compensating for a movement of an in-focus point caused by the zooming operation of the variable power lens;
first memory means for storing position information of the variable power lens and the focus lens;
control means for controlling the variable power lens and the focus lens; and
second memory means for storing current position information of the variable power lens and/or the focus lens,
wherein the control means determines, upon turning on a power supply of the lens assembly, whether the camera to which the lens assembly is mounted is the same as that in a previous operation, and if the camera is the same as that in the previous operation, the control means restores an operation state of the variable power lens and/or the focus lens at the time of turning off the power supply on the basis of the current position information stored in the memory means.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.